A diesel engine may include a turbocharger to extend the engine's power output capacity. The turbocharger may supply pressurized air to the engine so that the cylinder charge mass may be increased to increase engine output power. However, the engine may also operate at low engine air flows and boost pressures when a vehicle driver requests no torque to propel a vehicle. Further, a diesel engine may operate over a wide lean air-fuel ratio operating range. Consequently, diesel fuel injectors may have to supply a large range of fuel amounts to provide desired air fuel ratios over a range of operating conditions. Therefore, diesel fuel injectors are sized to supply fuel at high engine loads and low engine loads. Nevertheless, it may be difficult to provide small accurate amounts of fuel because of kinematics within the fuel injector and because of the fuel injector supplies a wide range of fuel injection amounts. It may be desirable to inject one or more small fuel injection amounts into a cylinder during a cylinder cycle to reduce combustion noise and control heat release of fuel being combusted. The small fuel injection amounts, which may be referred to as pilot injections, may be injected during the cylinder cycle, and the pilot injections may precede a main fuel injection during the cylinder cycle. If the pilot fuel injection amounts are inaccurate, engine combustion noise and hydrocarbon emissions may increase. In addition, it may be desirable to provide these small pilot fuel injections very close together in time, but fuel injectors also have injector off dwell times immediately after closing where the fuel injector cannot open. As such, it may not be possible for a fuel injector to provide pilot fuel injections as close together in time as may be desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a diesel fuel injection method, comprising: during a cycle of a cylinder, injecting diesel fuel to the cylinder via a low fuel flow rate diesel fuel injector and injecting diesel fuel to the cylinder via a high fuel flow rate diesel fuel injector via a controller, the low fuel flow rate diesel fuel injector and the high fuel flow rate diesel fuel injector positioned in the cylinder.
By supplying diesel fuel to a diesel engine via two different diesel fuel injectors having two different diesel fuel flow rates, it may be possible to supply accurate amounts of diesel fuel during pilot fuel injections and meet diesel fuel injection amounts at higher engine loads. In particular, pilot fuel injections may be provided by a lower flow fuel injector and main fuel injection amounts may be provided by a higher flow fuel injector. Further, the low fuel flow injector and the higher fuel flow injector may both supply main fuel injection pulses to provide desired engine air-fuel ratios at higher engine loads and higher engine speeds when fuel injection time may be short. In this way, the accuracy of injecting small fuel amounts and large fuel amounts during a cylinder cycle may be improved.
The present description may provide several advantages. Specifically, the approach may reduce engine emissions by improving accuracy of an amount of fuel delivered during a cylinder cycle. In addition, the approach may reduce engine combustion noise and/or control peak cylinder pressures. Further, the approach may provide more consistent engine operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.